FIG. 1 shows the construction of a typical conventional single-wafer CVD apparatus 10.
Referring to FIG. 1, the single-wafer CVD apparatus 10 includes a processing vessel 11 evacuated by a vacuum pump 13 via a shutdown valve 13A and a conductance valve 13B, wherein the processing vessel 11 includes therein a susceptor 12 having a heating mechanism (not shown) and holding thereon a substrate 12A to be processed. Thereby, the processing vessel 11 is provided with a showerhead 14 supplied with a source gas from a source gas supplying system 15 via a line L1 and a valve V1 such that the showerhead 14 faces the substrate 12A to be processed on the susceptor 12.
The source supplying system 15 includes source gas sources 15A-15C wherein the source gas in the source gas source 15A is supplied to the line L1 via a valve 15A while the source gas in the source gas source 15B is supplied to the line L1 via a valve 15VB. Further, the source gas in the source gas source 15C is supplied to the line L1 via a valve 15VC.
The source gas supplied via the line L1 is released to a processing space inside the processing vessel 11 via the showerhead 14, and desired film formation occurs at the surface of the substrate 12 to be processed as a result of the decomposition reaction taking place at the surface of the substrate 12A to be processed.
With the single-wafer CVD apparatus 10 of FIG. 1, there is provided a gate valve structure not illustrated on the processing vessel 11 for allowing loading and unloading of the substrate 12A to be processed, while the gate valve structure is coupled to a substrate transportation chamber. The single-wafer CVD apparatus 10 constructs a single-wafer substrate processing system together with other processing apparatuses coupled to the substrate transportation chamber.
With the single-wafer CVD apparatus 10 constituting such a single-wafer processing system, the substrate temperature is controlled during the film forming processing by a heating device formed in the susceptor 12 while the wall surface of the processing vessel 10 is maintained at a relatively low temperature from room temperature to 150° C. (cold wall).
With such a cold wall type CVD apparatus, it is inevitable that there is caused some deposition of reactants on the inner wall surface of the processing vessel 11 at the time of film deposition on the substrate 12A to be processed, and thus, it has been practiced to conduct a cleaning process for removing the deposits by causing to flow a cleaning gas acting an etchant to the interior of the processing vessel 11 each time film formation processing for one or plural substrates has been completed.
Particularly, with the CVD apparatuses used for fabrication of ultra-miniaturized semiconductor devices of these days, it is preferable to conduct the cleaning process as frequently as possible, ideally each time a substrate is processed, for recovering the predetermined initial processing condition. However, when such frequent cleaning processing has been conducted, the cleaning time associated with the cleaning processing causes serious decrease in the throughput of semiconductor production.
Thus, with the CVD apparatus of FIG. 1, there is provided a cleaning module outside the processing vessel 11 such that the cleaning module includes an etching gas source 16A, a plasma gas source 16B and a remote plasma source 16C, and a highly reactive etching gas formed by the remote plasma source 16C is introduced into the processing space inside the processing vessel 11 via the line L2 and the valve 16Vc. By providing the plasma source at the outside of the processing vessel 11, damaging of the inner wall of the processing vessel 11 by high energy plasma is avoided, and it becomes possible to conduct stable cleaning process. Further, with such a construction, the ions formed in the plasma cause recombination with electrons as they are transported from the remote plasma source 16C to the processing vessel 11, and thus, only the radicals that promote the reaction are supplied to the processing vessel 11 with the construction of FIG. 1.
In FIG. 1, it should be noted that the etching gas source 16A supplies an etching gas containing fluorine such as NF3 to the remote plasma source 16C via a valve 16VA, while the plasma gas source 16B supplied a rare gas such as Ar to the remote plasma source 16C via a valve 16VB.
For the cleaning gas containing fluorine, it is also possible to use a non-halogen compound such as CH3COOH, in addition to the halogen compound such as NF3. Further, it is possible to use He, Ne, Kr, Xe, or the like, for the diluting gas from the plasma gas source 16B in place of Ar. Further, the diluting gas is not limited to a rare gas and it is also possible to use the gases such as H2O, O2, H2, N2, C2F6, or the like, for the diluting gas.
With regard to such a remote plasma source 16C, it is possible to use any of an induction coupled type plasma (ICP) generator 20 shown in FIG. 2A, an electron cyclotron resonance (ECR) type plasma generator shown in FIG. 2B, a helicon wave-excited plasma generator 40 shown in FIG. 2C, a microwave cavity type plasma generator shown in FIG. 2D, a toroidal type plasma generator 60 shown in FIG. 2E, and the like. Further, a capacitive-coupling plasma (CCP) generator 70 shown in FIG. 3 is used as the plasma source that is provided inside the processing vessel 11.
With the ICP type plasma generator 20 of FIG. 2A, a high-frequency coil 22 is wound around a plasma vessel 21, in which the plasma is generated, and plasma is formed inside the plasma vessel by driving the high-frequency coil 22 by a high-frequency power source 23.
With the ECR plasma generator 30 of FIG. 2B, magnets 32 are disposed around the plasma vessel 31 such that a magnetic field is applied to the space inside the plasma vessel 31, and electron cyclotron resonance is induced in the gas inside the vessel 31 by supplying a microwave power to the gas inside the processing vessel 31 from a microwave source 33.
With the helicon-wave type plasma generator 40 of FIG. 2C, a magnet 44 is provided close to the processing vessel 41 in which generation of plasma is to be achieved, and a loop antenna 42 is provided in the vicinity of the plasma vessel 41. By driving the loop antenna by a high-frequency power from a high-frequency power source 43, a helicon wave is propagated through the plasma vessel 41 and it becomes possible to realize a high-density plasma.
With the microwave cavity type plasma generator 50 of FIG. 2D, the plasma vessel 51, in which the plasma is formed, constitutes a microwave cavity, and plasma is formed by driving the microwave cavity by a microwave electric field from a microwave source 52.
With the toroidal plasma generator 60 of FIG. 2E, there is provided a cyclic gas passage 61 having a gas entrance 61A and a gas outlet 61B, and high-frequency coil is wound outside the gas passage 61.
Thus, a rare gas such as Ar introduced into the gas passage 61A circles around the cyclic gas passage 61, wherein plasma is induced in the rare gas by driving the high-frequency coil 62 by a microwave.
With the CCP-type plasma generator 70 of FIG. 3, there are disposed a pair of parallel plate electrodes 71A and 71B inside a plasma vessel 71 in which plasma is formed, and plasma is formed between the foregoing electrodes by driving the electrodes 71A and 71B by a high-frequency power source 72. Thus, the plasma generator 70 of FIG. 3 itself constitutes the plasma generator and the plasma vessel 71 is used for the processing vessel. In this case, the lower electrode 71B is used for the susceptor and the substrate to be processed is placed on the lower electrode 71B.
Particularly, with the toroidal plasma generator of FIG. 2E, there are obtained various advantageous features such as plasma generation taking place at a location offset from the wall surface of the generator, and introduction of charged particles of large mass such as ions into the processing space inside the processing vessel 11 being suppressed. Thus, it is thought preferable to use such a toroidal plasma generator in the plasma processing apparatus 10 of FIG. 1 as the remote plasma source 16C.
FIG. 4 shows the toroidal plasma generator 60 shown in FIG. 2E for used as the remote plasma source 16C in detail.
Referring to FIG. 4, the plasma generator 60 includes the cyclic gas passage 61 having the gas entrance 61A and the gas outlet 61B and the high-frequency coil 62 is wound around at the outside of the gas passage.
Thus, the rare gas such as Ar introduced into the gas entrance 61A circles around the circular gas passage 61, and plasma is induced in the foregoing rare gas by driving the high-frequency coil 62 by a high-frequency power. Thereby, there is formed a cyclic current path shown in FIG. 4 by a continuous line 61a in the gas passage 61 as the plasma thus induced circles around the gas passage 61 at high speed, and the line of magnetic force formed by the high-frequency coil is pinched down to a path coincident to the current path 61a as shown in FIG. 4 by a broken line 61b. With such pinching down of the line of magnetic force to the path 61b, there occurs corresponding pinching down of the electrons and ions in the plasma to the current path 61a, which is coincident to the path 61b of the line of magnetic force, resulting in further increase of the current density in the current path 61a. Such increase of the current density invites further pinching of the line of magnetic down to the path 61b for the line of magnetic force.
Thus, with the toroidal plasma generator 60 of FIG. 4, the high-density plasma is formed at the location offset from the wall surface that defines the cyclic gas passage 61, and because of this, there occurs little sputtering in the wall surface by the electrons accelerated to high energy state. Thereby, plasma formation occurs with little contamination, and the plasma thus formed with little contamination is maintained stably.    PATENT REFERENCE 1 U.S. Pat. No. 6,374,831.